The political movement began in 1922 when Francesc Macià founded Estat Català (Catalan State). In 1931, Estat Català and other parties formed Esquerra Republicana de Catalunya (Republican Left of Catalonia; ERC), which won a dramatic victory in the municipal elections of that year. Macià proclaimed a Catalan Republic, but after negotiations with the leaders of the new Spanish Republic, he instead accepted autonomy within the Spanish state. In the Spanish Civil War, General Francisco Franco abolished Catalan autonomy in 1938. Following Franco's death in 1975, Catalan political parties concentrated on autonomy rather than independence.

The modern independence movement began when the 2006 Statute of Autonomy, which had been agreed with the Spanish government and passed by a referendum in Catalonia, was challenged in the Spanish High Court of Justice, which ruled that a large number of articles were unconstitutional, or were to be interpreted restrictively. Popular protest against the decision quickly turned into demands for independence. Starting with the town of Arenys de Munt, over 550 municipalities in Catalonia held symbolic referendums on independence between 2009 and 2011, all of them returning a high "yes" vote. A 2010 protest demonstration against the court's decision, organised by the cultural organisation Òmnium Cultural, was attended by over a million people. The popular movement fed upwards to the politicians; a second mass protest on 11 September 2012 (the National Day of Catalonia) explicitly called on the Catalan government to begin the process towards independence. Catalan president Artur Mas called a snap general election, which resulted in a pro-independence majority for the first time in the region's history. The new parliament adopted the Catalan Sovereignty Declaration in early 2013, asserting that the Catalan people had the right to decide their own political future.

The Catalan government announced a referendum, to be held in November 2014, on the question of statehood. The referendum was to ask two questions: "Do you want Catalonia to become a State?" and (if yes) "Do you want this State to be independent?" The Spanish government referred the proposed referendum to the Spanish Constitutional Court, which ruled it unconstitutional. The Catalan government then changed it from a binding referendum to a non-binding "consultation". Despite the Spanish court also banning the non-binding vote, the Catalan self-determination referendum went ahead on 9 November 2014. The result was an 81% vote for "yes-yes", but the turnout was only 42%. Mas called another election for September 2015, which he said would be a plebiscite on independence. Pro-independence parties fell just short of a majority of votes in the September election, although they won a majority of seats. The new parliament passed a resolution declaring the start of the independence process in November 2015, and the following year, new president Carles Puigdemont announced a binding referendum on independence, to be held in September 2017. The Spanish government continues to oppose any move in the direction of Catalan independence.

The first pro-independence political party in Catalonia was Estat Català (Catalan State), founded in 1922 by Francesc Macià.[8] Estat Català went into exile in France during the dictatorship of Primo de Rivera (1923–1930), launching an unsuccessful uprising from Prats de Molló in 1926.[9] In March 1931, following the overthrow of Primo de Rivera, Estat Català joined with the Partit Republicà Català (Catalan Republican Party) and the political group L'Opinió (Opinion) to form Esquerra Republicana de Catalunya (Republican Left of Catalonia; ERC), with Macià as its first leader.[10] The following month, the ERC achieved a spectacular victory in the municipal elections that preceded the 14 April proclamation of the Second Spanish Republic.[11] Macià proclaimed a Catalan Republic on 14 April, but after negotiations with the provisional government he was obliged to settle for autonomy, under a revived Generalitat of Catalonia.[12] Catalonia was granted a statute of autonomy in 1932, which lasted until the Spanish Civil War. In 1938 General Franco abolished both the Statute of Autonomy and the Generalitat.[2]

Following Franco's death in 1975, Spain moved to restore democracy. A new constitution was adopted in 1978, which asserted the "indivisible unity of the Spanish Nation", but acknowledged "the right to autonomy of the nationalities and regions which form it".[17] Independence parties objected to it on the basis that it was incompatible with Catalan self-determination, and formed the Comité Català Contra la Constitució Espanyola (Catalan Committee Against the Consitution) to oppose it.[16] The constitution was approved in a referendum by 88% of voters in Spain overall, and just over 90% in Catalonia.[18] It was followed by the Statute of Autonomy of Catalonia of 1979, which was approved in a referendum, with 88% of voters supporting it.[19] This led to the marginalisation or disappearance of pro-independence political groups, and for a time the gap was filled by militant groups such as Terra Lliure.[20]

In 1981, a manifesto issued by intellectuals in Catalonia claiming discrimination against the Castilian language drew a response in the form of published letter, Crida a la Solidaritat en Defensa de la Llengua, la Cultura i la Nació Catalanes (Call for solidarity in defence of the Catalan language, culture and nation), which called for a mass meeting at the University of Barcelona, out of which a popular movement arose. The Crida organised a series of protests that culminated in a massive demonstration in the Camp Nou on 24 June 1981.[21] Beginning as a cultural organisation, the Crida soon began to demand independence.[22] In 1982, at a time of political uncertainty in Spain, the Ley Orgánica de Armonización del Proceso Autonómico (LOAPA) was introduced in the Spanish parliament, supposedly to "harmonise" the autonomy process, but in reality to curb the power of Catalonia and the Basque region. There was a surge of popular protest against it. The Crida and others organised a huge rally against LOAPA in Barcelona on 14 March 1982. In March 1983, it was held to be ultra vires by the Spanish Constitutional Court.[22] During the 1980s, the Crida was involved in nonviolent direct action, among other things campaigning for labelling in Catalan only, and targeting big companies.[21] In 1983, the Crida's leader, Àngel Colom, left to join the ERC, "giving an impulse to the independentist refounding" of that party.[23]

Following elections in 2003, the moderate nationalist Convergència i Unió (CiU), which had governed Catalonia since 1980, lost power to a coalition of left-wing parties composed of the Socialists' Party of Catalonia (PSC), the pro-independence Esquerra Republicana de Catalunya (ERC) and a far-left/Green coalition (ICV-EUiA), headed by Pasqual Maragall. The government produced a draft for a new Statute of Autonomy, which was supported by the CiU and was approved by the parliament by a large majority.[24] The draft statute then had to be approved by the Spanish parliament, which could make changes; it did so, removing clauses on finance and the language, and an article stating that Catalonia was a nation.[25] When the amended statute was put to a referendum on 18 June 2006, the ERC, in protest, called for a "no" vote. The statute was approved, but turnout was only 48.9%.[26] At the subsequent election, the left-wing coalition was returned to power, this time under the leadership of José Montilla.[24]

The Partido Popular, which had opposed the statute in the Spanish parliament, challenged its constitutionality in the Spanish High Court of Justice. The case lasted four years.[27] In its judgement, issued on 18 June 2010, the court ruled that fourteen articles in the statute were unconstitutional, and that 27 others were to be interpreted restrictively. The affected articles included those that gave preference to the Catalan language, freed Catalonia from responsibility for the finances of other autonomous communities, and recognised Catalonia as a nation.[27][28] The full text of the judgement was released on 9 July 2010, and the following day a protest demonstration organised by the cultural organisation Òmnium Cultural was attended by over a million people, and led by José Montilla.[27][28]

During and after the court case, a series of symbolic referendums on independence were held in municipalities throughout Catalonia. The first of these was in the town of Arenys de Munt on 13 September 2009. About 40% of eligible voters participated, of whom 96% voted for independence.[29] In all, 552 towns held independence referendums between 2009 and 2011.[30] These, together with demonstrations organised by Òmnium Cultural and the Assemblea Nacional Catalana (ANC), represented a "bottom-up" process by which society influenced the political movement for independence.[30] At an institutional level, several municipalities of Catalonia came together to create the Association of Municipalities for Independence, an organisation officially established on 14 December 2011 in Vic which brought local organisations together to further the national rights of Catalonia and promote its right to self-determination.[31] The demonstration of 11 September 2012 explicitly called on the Catalan government to begin the process of secession.[32] Immediately after it, Artur Mas, whose CiU had regained power in 2010, called a snap election for 25 November 2012, and the parliament resolved that a referendum on independence would be held in the life of the next legislature.[33] Although the CiU lost seats to the ERC, Mas remained in power.[33]

Mas and ERC leader Oriol Junqueras signed an agreement by which the ERC would support the CiU on sovereignty issues while on other matters it might oppose it. The two leaders drafted the Declaration of Sovereignty and of the Right to Decide of the Catalan People, which was adopted by the parliament at its first sitting in January 2013. The declaration stated that "the Catalan people have, for reasons of democratic legitimacy, the nature of a sovereign political and legal subject", and that the people had the right to decide their own political future.[33] The Spanish government referred the declaration to the Spanish Constitutional Court, which ruled in March 2014 that the declaration of sovereignty was unconstitutional; it did, however, allow that there existed a right to decide.[34] On 11 September 2013, an estimated 1.6 million demonstrators formed a human chain, the Catalan Way, from the French border to the regional border with Valencia.[35] The following month, the CiU, the ERC, the ICV-EUiA and Candidatura d'Unitat Popular (CUP) agreed to hold the independence referendum on 9 November 2014, and that it would ask two questions: "Do you want Catalonia to become a State?" and (if yes) "Do you want this State to be independent?".[36] A further mass demonstration, the Catalan Way 2014, took place on 11 September 2014, when protesters wearing the Catalan colours of yellow and red filled two of Barcelona’s avenues to form a giant "V", to call for a vote.[37] Following the Constitutional Court’s ruling, the Catalan government changed the vote to a "process of citizen participation" and announced that it would be supervised by volunteers.[36] The Spanish government again appealed to the Constitutional Court, which suspended the process pending the appeal, but the vote went ahead.[38] The result was an 81% vote for yes-yes, but the turnout was only 42%, which could be seen as a majority opposed to both independence and the referendum.[39] Criminal charges were subsequently preferred against Mas and others for defying the court order.[38]

In June 2015 the CiU broke up as a result of disagreement between its constituent parties – Convergència Democràtica de Catalunya (CDC) and Unió Democràtica de Catalunya (UDC) – over the independence process. Mas’s CDC joined with the ERC and other groups to form Junts pel Sí (Together for "Yes"), which announced that it would declare independence if it won the election scheduled for September.[40] In the September election, Junts pel Sí and the CUP between them won a majority of seats, but fell short of a majority of votes, with just under 48%.[41] On 9 November 2015, the parliament passed a resolution declaring the start of the independence process, proposed by Junts pel Sí and the CUP.[42] In response, Spanish premier Mariano Rajoy said that the state might "use any available judicial and political mechanism contained in the constitution and in the laws to defend the sovereignty of the Spanish people and of the general interest of Spain", a hint that he would not stop at military intervention.[43] Following prolonged negotiations between Junts pel Sí and the CUP, Mas was replaced as president by Carles Puigdemont in January 2016. Puigdemont, on taking the oath of office, omitted the oath of loyalty to the king and the Spanish constitution, the first Catalonian president to do so.[43]

Further pro-independence demonstrations took place in Barcelona in September 2015, and in Barcelona, Berga, Lleida, Salt and Tarragona in September 2016. In late September 2016, Puigdemont told the parliament that a binding referendum on independence would be held in the second half of September 2017, with or without Madrid's consent.[44]

Neither the Spanish state, the European Union, the United Nations nor any sovereign state question Spain's de facto and de jure sovereignty over Catalonia or any other of Spain's autonomous regions. Only Spain's territories in North Africa are subject to irredentist claims by Morocco.

The legality of any Spanish constituent country attaining de facto independence or declaring unilateral independence outside the framework of Spanish constitutional convention is debatable. Under international law, a unilateral declaration might satisfy the principle of the "declarative theory of statehood", but not the "constitutive theory of statehood". Some legal opinion following the Supreme Court of Canada's decision on what steps Quebec would need to take to secede is that Catalonia would be unable to unilaterally declare independence under international law, even in the currently unlikely event that the Spanish government permitted a referendum on an unambiguous question on secession.[45][46]

The think tankCercle d'Estudis Sobiranistes, led by the jurists Alfons López Tena and Hèctor López Bofill was founded in 2007. Since then it has summoned a number of lawmakers, professors, businessmen, professionals, economists, journalists and intellectuals for the cause of Catalonia's independence.

All Spanish parties in Catalonia reject the idea of independence. Ciutadans[66] and the People's Party of Catalonia,[67] which had 17.9% and 8.5% of the vote respectively in the 2015 Catalan parliamentary election, have always opposed the notion of Catalan self-determination. The Socialists' Party (12.7% of vote) opposes independence as well. While some of its members supported the idea of a self-determination referendum up until 2012,[68] the official position as of 2015 is that the Spanish Constitution should be reformed in order to better accommodate Catalonia.[69] A majority of voters of left-wing platform Catalonia Yes We Can (8.94%) reject independence although the party favours a referendum in which it would campaign for Catalonia remaining part of Spain. CDC's former Catalanist partner Unió came out against independence and fared badly in the 2015 elections, although polls show a rebound in voter support as the institutional crisis deepens.

The position of Catalans regarding the independence of either Catalonia must be studied taking into account an important fact, namely, that a large number of Catalan citizens are of immigrant origin and that many of them feel little or no connection to the Catalan language or culture. It has been calculated that the total population of Catalonia, with no migration from other parts of Spain, would have grown from 2 million people in 1900 to just 2.4 million in 1980,[75] merely 39% of the actual population of 6.1 million at that date. In the 1970s, there were nearly 900,000 residents in Catalonia from Andalusia.[76] This inflow has been the primary driver of population growth in Catalonia which stood at over 7.4 million in 2009, a majority of which are of at least partial non-Catalan Spanish ancestry.

One study found that support for independence is a function of grievances rooted in the desire for Catalonia to assume responsibility for taxation and spending policy. This suggests that Spain might be able to stave off Catalonia's separatist bid through some form of political and taxation policy reconfiguration.[77]

Several institutions have performed polls which also include questions on the independence issue in Catalonia. The following are the most prominent ones are the Center for Opinion Studies (Centre d'Estudis d'Opinió; CEO), the Spanish government-run Social Research Centre (Centro de Investigaciones Sociales; CIS) and the Social and Political Sciencies Institute of Barcelona (Institut de Ciències Polítiques i Socials; ICPS) belonging to the Autonomous University of Barcelona and Diputation of Barcelona.

The CEO was depending on the Economy Department of the Generalitat of Catalonia until early 2011. Since then it has been placed under direct control of the Presidency of the Generalitat and is currently headed by Jordi Argelaguet i Argemí. Since the second quarter of 2011, CEO has conducted polls regarding public sentiments toward independence.

In addition, CEO performs regular polls studying opinion of Catalan citizens regarding Catalonia's political status within Spain. The following table contains the answers to the question "Which kind of political entity should Catalonia be with respect to Spain?":[94]

CIS performed a poll in Catalonia in 2001, including an explicit question on independence with the following results: 35.9% supporting it, 48.1% opposing it, 13.3% indifferent, 2.8% did not reply[citation needed].